refactor: wire helpers into ComfyPage and update test usages

Phase 2 of ComfyPage refactor:

- Add ToastHelper, DragDropHelper, CommandHelper instances to ComfyPage

- Remove migrated methods from ComfyPage (command, toast, dragDrop, workflow, canvasOps, nodeOps methods)

- Update all test files to use new helper paths

- Keep visibleToasts as passthrough getter for backward compatibility

Amp-Thread-ID: https://ampcode.com/threads/T-019c1666-ed27-773c-976a-07cc805d7a6c
Co-authored-by: Amp <amp@ampcode.com>

browser_tests/tests/domWidget.spec.ts

@@ -34,7 +34,7 @@ test.describe('DOM Widget', { tag: '@widget' }, () => {
     { tag: '@screenshot' },
     async ({ comfyPage }) => {
       await comfyPage.settings.setSetting('Comfy.UseNewMenu', 'Top')
-      await comfyPage.executeCommand('Workspace.ToggleFocusMode')
+      await comfyPage.command.executeCommand('Workspace.ToggleFocusMode')
       await comfyPage.nextFrame()
       await expect(comfyPage.canvas).toHaveScreenshot('focus-mode-on.png')
     }